This invention relates to a dispensing apparatus for dispensing drinking water for domestic or business use with a function of purifying and sterilizing raw water such as tap water and groundwater.
As conventional dispensing apparatuses of the type, a beverage dispenser for dispensing or vending a cup of coffee or a carbonic beverage and a tea server for serving a cup of tea are known and widely used. Each of the beverage dispenser and the tea server is provided with a water purification unit.
By way of example, the beverage dispenser will be described. The beverage dispenser comprises the water purification unit for purifying raw water such as tap water to produce purified water, and a beverage unit for producing the beverage such as the coffee or the carbonic beverage by the use of the purified water produced by the water purification unit. In response to a predetermined vending operation performed in the beverage unit, the beverage is vended or dispensed. The beverage dispenser further comprises a pressure detector disposed in a pipeline for feeding the purified water from the water purification unit to the beverage unit. The pressure detector detects a water pressure within the pipeline as a pipeline water pressure. When the vending operation is performed in the beverage unit, the purified water flows through the pipeline so that the pipeline water pressure is changed. Thus, the pressure detector detects the flow of the purified water, i.e., the occurrence of the vending operation in the beverage unit to open a water supply valve which is normally-closed electromagnetic valve and serves as a source valve of the water purification unit.
As described above, when the vending operation is performed in the beverage unit, it is detected by the pressure detector to open the water supply valve. Thus, the beverage using the purified water is vended.
In the above-mentioned conventional dispensing apparatus, whether or not the vending operation is carried out in the beverage unit is detected by the pressure detector. Therefore, the timing of operating the water supply valve is greatly affected by a local water pressure which has different values between districts or places where the dispensing apparatus is installed.
Referring to FIG. 1, a dispensed amount of the beverage in terms of the number of cups and the pipeline water pressure are plotted in an abscissa and an ordinate, respectively. Specifically, it is assumed that the local water pressure of the tap water is high at the place or in the district where the dispensing apparatus is installed. In this event, the pipeline water pressure is already kept high in a standby state before the vending operation is started. For example, if the pipeline is formed by a flexible tube, the flexible tube is expanded because of such a high pipeline water pressure. When a pouring port at the end of the dispensing apparatus is opened during the vending operation, the dispensed amount corresponding to three cups is supplied in a single vending operation as depicted by a solid line in the figure. In addition, a pressure difference is great between one vending operation and a next vending operation. Therefore, the dispensed amount varies between successive vending operations. In the next vending operation, the water supply valve is opened again to flow tap water through the water purification unit into the pipeline. At this time, a difference between a flow-in pressure of the tap water and the pipeline water pressure is extremely great. This results in a phenomenon known as the "water hammer".
On the contrary, if the local water pressure of the tap water is low at the place or in the district where the dispensing apparatus is installed, the pressure detector must have ON and OFF set values which are considerably low with a small difference therebetween as depicted by a two-dot-and-dash line in FIG. 1. Such setting is difficult and troublesome. If the set values are set in correspondence to a normal water pressure, the pressure detector always produces an open signal to the water supply valve irrespective of whether or not the vending operation is performed. Therefore, the water supply valve is always kept energized and opened. This often results in a disorder of the water supply valve. In addition, if the water supply valve is always kept opened, bacteria are allowed to intrude through the pouring port of the beverage unit to contaminate the tap water as the raw water. Thus, a sanitary problem arises. Furthermore, upon occurrence of water leakage in the dispensing apparatus, such water leakage will uninterruptedly last if the water supply valve is always kept opened. Therefore, an additional arrangement is required to avoid the water leakage.
In case where the set values of the pressure detector are slightly lower than the local water pressure of the tap water, the water supply valve is very frequently opened and closed as depicted by a dash-and-dot line in FIG. 1 to cause the so-called chattering. This shortens the lifetime of the water supply valve.